There are display devices equipped with touch panels attached capable of inputting, by handwriting, data such as characters and graphics using a touch pen. In this kind of display device equipped with a touch panel, a user draws a character, graphic, or the like that the user wants to input with the touch pen on the touch panel, thereby causing the data related to the character, graphic, or the like to be inputted into the display device equipped with a touch panel, and the inputted data is displayed on a display surface of the display device equipped with a touch panel.
Touch panels are known to use a resistance film system, electrostatic capacitance system, infrared light system, or the like. Recently, many electrostatic capacitance system touch panels capable of being implemented at low cost with excellent durability are being used.
Electrostatic capacitance system touch panels each have diamond-shaped X-axis patterned detection electrodes and Y-axis patterned detection electrodes that are disposed in a lattice shape such that the X-axis patterned detection electrodes and the Y-axis patterned detection electrodes do not overlap in a plan view. The electrostatic capacitance system touch panels detect a touch point (a point touched by a touch pen, finger, or the like) by using the X-axis patterned detection electrodes and the Y-axis patterned detection electrodes to detect a change in the electric field generated from touching any point on the electrostatic capacitance system touch panel with the touch pen.
In electrostatic capacitance system touch panels, if a touch point is away from the vicinity of the center of the X-axis patterned detection electrodes and the Y-axis patterned detection electrodes, the accuracy for detecting the touch point position is increased by detecting position information for the touch point using interpolation (see Patent Document 1, Japanese Patent Application Laid-Open Publication No. H7-13681, for example).